Dry eye is a chronic disease, which is caused by various factors, on lacrimal fluid and corneal/conjunctival epithelium and is an ocular disease accompanied by ocular discomfort and dysfunction. The number of dry eye patients in Japan is estimated to be 20 million. Examples of a medicament for treating dry eye are limited to sodium hyaluronate eye drops and/or administration of artificial lacrimal fluid, but a medicament comprising diquafosol sodium or rebamipide as an active ingredient and having an action of enhancing secretion of mucin from a conjunctival tissue have become commercially available. Among the mucins, Muc5ac is a protein that is secreted from goblet cells of an ocular conjunctival tissue, and is an important component constituting lacrimal fluid. A decrease in the amount of mucin is one of factors causing dry eye.
Meanwhile, cyclo-trans-4-L-hydroxyprolyl-L-serine is a hydroxyproline derivative, and has been known to have cell proliferation and cell protection actions (Patent Literature 1) and to be effective in preventing or treating allergic and inflammatory diseases (Patent Literatures 2 and 3).